This invention relates to filters and seals used in solenoid valves. Such valves are commonly used in commercial, institutional and public washrooms where sensor-controlled fixtures such as faucets, showerheads and the like are provided. A sensor associated with a fixture senses the presence or departure of a user and sends an appropriate electrical signal to one or more solenoid valves in the water supply lines to open or close, thereby starting and stopping water flow as needed. Some solenoid valves use a control bypass which utilizes the water pressure to assist in closing the valve. All solenoid valves have a valve seat and some type of closure member which opens or closes the valve seat to start and stop flow. The control bypass and the valve seat must be kept clear of particles or debris to prevent clogging. Particles deposited on these sensitive areas can cause the valve to leak, or even worse, they can prevent the valve from opening or closing. Filters are used to prevent particles from clogging of the control bypass or from being deposited on the seat. A typical filter includes a cylindrical screen placed in or near the inlet to the valve.
However, filters have problems of their own. Particular attention must be paid to sealing the ends of the filter to prevent particles from bypassing the filter altogether. In the past, two approaches to this problem have been used. The first approach is to physically compress the filter screen on its ends by tightening a cap or the like. This makes the screen usable one time only. That is, when the valve is opened for maintenance the screen that has been deformed cannot subsequently be compressed the way it was when it was new. Replacing this type of filter in the field is very difficult because of the torque required to compress the filter and make a seal with the valve cap.
The second approach found in the prior art is to put a rubber seal on each end of the filter. But there is no good way to attach a rubber seal to what is usually a metal mesh filter screen. Experience shows that the rubber seals tend to fall off if the filter is removed during maintenance. Attempts to mold seals on the ends of a screen are restricted by the geometry of the part. A cylindrical filter screen cannot have seals molded on to its ends. In addition, molding a seal on to a screen can not be easily controlled. During the molding cycle the rubber tends to flash into what is intended to be the open area of the screen, thus reducing the available filter area. Seals formed separately from the filter screen can be placed on the ends of the filter screens in the factory, but there is no good way to retain them in the desired position in the field. Gluing individual rubber seals to the ends of the filter screen has been tried without success. They come off the filter screen in the field. Installers would either not notice this or incorrectly install the rubber seals. Eventually particles would bypass the filter and cause the valve to malfunction as mentioned above. What is needed is a seal for a filter that will not come apart in the field.